Death Valley geology field trip

Split Cinder Cone

Aerial view of Split Cinder Cone. This small cinder cone is a striking example of the dynamic forces that have shaped Death Valley. Photo by Tom Bean, NPS.

Birth of a cinder cone

Less than 300,000 years ago, a chamber filled with solid crystals and searing molten basaltic rock simmered beneath Death Valley. Magma rose toward the surface, following weaknesses in the Earth's crust. Nearing the surface, the black lava encountered the fractured earth of the Death Valley Fault zone.
Lava quickly made its way through the fault-weakened rock and burst out of the valley floor as a fiery fountain of scorching lava and gas. Lava fountains threw blobs of molten basalt hundreds of feet into the air. Although lava erupted at 1200°C (2200°F), most of the molten, airborne globs cooled and solidified to form cinders before reaching the ground. Most cinders fell very near the central vent, building a small cone.

What did the initial eruption of Split Cinder cone look like? The image at left of a fountain of fire erupting at Pu`u `O`o cinder cone, Hawaii might help you imagine it.

Cinder by cinder

Most cinders fell very near the central vent. Layer upon layer of volcanic ejecta were deposited, building a higher and steeper cinder cone. Eventually the cone became so steep that the flanks collapsed under their own weight. The collapsing cinders came to rest when the sides reached just the right steepness to keep them stable. This angle, usually about 35°, is called the angle of repose.

Every pile of loose particles has a unique angle of repose, depending upon the material it's made from. Because all volcanic cinders have almost the same angle of repose, cinder cones everywhere develop nearly identical shapes with nice, straight sides rising at an angle of about 35° from the ground. Cinder cones are commonly very symmetrical. Split Cinder Cone may have once looked very much like Pu`u ka Pele cinder cone at right.
The birth of this small cinder cone is only part of it's intriguing story. How did this once-symmetrical cone split into two pieces? Click here to continue.